1. Field of the Invention
The present invention relates to a coating apparatus for applying a coating solution to a rotating target substrate, and a method therefor.
2. Description of the Related Art
In general, in the manufacturing process of a liquid crystal display (LCD) device, an ITO (Indium Tin Oxide) thin film, an electrode pattern, and the like are formed on an LCD substrate (glass substrate). For this formation, a series of processing operations are performed in which the circuit pattern and the like are reduced and transferred on a photoresist by using a photolithography technique similar to that used in the semiconductor manufacturing process, and the transferred circuit pattern and the like are developed.
For example, after a rectangular LCD substrate as the target substrate is cleaned by a cleaning unit, the LCD substrate is subjected to a hydrophobic process by an adhering unit, and is cooled by a cooling unit. Then, a photoresist film, i.e., a photosensitive film, is formed on the LCD substrate by coating with a resist coating apparatus. The photoresist is baked by heating with a heating unit, and a predetermined pattern is exposed by an exposure unit. A developing solution is applied to the exposed LCD substrate, and the LCD substrate is developed by a developing unit, and the developing solution is washed out with a rinsing solution, thus completing the developing operation.
This resist coating is generally performed in accordance with the spin coating scheme by using a coating apparatus disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 63-248471.
A cleaning solution supply pipe extends through the fixing collar from the outside, and a cleaning solution nozzle at the distal end of the cleaning solution supply pipe is located below the spin chuck. If the resist solution is left attaching to the inner wall of the rotary cup, part of the resist solution is removed to undesirably form particles. Therefore, for example, every time one cassette is processed, the spin chuck is moved upward, the cleaning solution nozzle is located between the spin chuck and the bottom surface of the rotary cup, and the spin chuck and the rotary cup are rotated while spraying a cleaning solution, e.g., thinner, thereby cleaning the inner surface of the rotary cup.
However, the coating apparatus described above has problems as follows.
(1) The fixing collar is interposed for the purpose of extending the cleaning solution supply pipe from the outside of the rotation mechanism. The inner rotary cylinder serving as the rotating shaft of the spin chuck and the outer rotary cylinder serving as the rotating shaft of the rotary cup are provided on the two sides of the fixing collar, and the spin chuck and the rotary cup are rotated by the separate driven pulleys. Thus, during acceleration or deceleration, the rotational speeds of the spin chuck and rotary cup differ often. More specifically, as a rotary cup generally has a large weight, a belt used for rotating this cup tends to be stretched. As a result, rotation of the pulleys cannot accurately catch up with rotation of this belt during acceleration, and the rotational speed of the pulleys becomes higher than the traveling speed of the belt due to the inertia force during deceleration. For this reason, a relative rotation occurs between the spin chuck and the bottom surface of the rotary cup to rub the seal member. Then, the seal member undesirably forms particles.
(2) As the inner and outer rotary cylinders are respectively provided to the inner and outer sides of the fixing collar, the mechanism of the rotating shaft forms a double structure which is complicated.